This invention relates in general to photovoltaic cells adapted to absorb photons in a selected bandgap for conversion to electricity and, more specifically, to a method of producing a thin-film, back-surface-reflector coplanar contact solar cell comprising gallium arsenide.
With the continuing increases in the cost and availability of energy has come increased interest in photovoltaic cells useful in solar cell arrays to convert the sun's radiation directly into electricity. A number of problems have, however, limited the usefulness of such direct energy conversion solar cells.
Most of the known photo electric materials have low efficiencies, generally well below 20%. Also, the materials tend to be expensive and the devices difficult and expensive to fabricate in the sizes required to generate appreciable quantities of electricity. Photons in bands outside the absorption bandgap of the specific photo electric material tend to be absorbed in the cell and converted to waste heat which degrades the cell output and must be carried away. Terrestrial solar cell arrays further suffer from a reduction in impinging solar energy due to atmospheric haze, clouds and night time.
Space based arrays have been proposed to overcome these problems, both for use where electrical energy is required in space, e.g., powering a space station, and for retransmission to earth, e.g., through microwave transmitters and receivers. Between the relatively high weight and low efficiency of present solar cell designs and photovoltaic materials, large space based solar cell arrays have not yet become economically feasible.
Thus, there is a continuing need for improvements in the manufacture of solar cells and photovoltaic materials, especially for use in space.